Secondary batteries such as non-aqueous electrolyte secondary batteries, nickel-metal hydride secondary batteries, and nickel-cadmium secondary batteries are used as a power source for driving a variety of apparatus. Secondary batteries have various uses from consumer apparatus exemplified by cellular phones to electric vehicles, electric tools and the like. Above all, non-aqueous electrolyte secondary batteries attract a great attention because they are small-sized, light-weight, and have a high energy density. In recent years, development of the secondary batteries having a higher energy density and a higher output has been increased.
A secondary battery used for consumer apparatus, for example a non-aqueous electrolyte secondary battery includes in general a metallic battery case having a bottom for housing an electrode group and an electrolyte, and a sealing plate for sealing an opening of the battery case. The sealing plate includes a metallic filter serving as an internal terminal and a metallic cap serving as an external terminal, and a safety valve and a PTC element are usually interposed between these. The safety valve is composed of a metal thin film and an explosion-proof valve, for example. The sealing plate is formed by caulking the periphery of the metallic filter on the periphery of the metallic cap, the PTC element, and the safety valve with an inner gasket made of resin interposed therebetween.
The metal thin film and the explosion-proof valve constituting the safety valve are welded at respective central portions and are electrically connected. In the case where a battery is erroneously overcharged and an internal pressure of the battery is abnormally increased, the metal thin film breaks to block the current path. At this time, gas inside the battery is discharged outside. For high output purposes requiring discharging at a large current, it is necessary to secure such a safety function and generate a large current efficiently by inhibiting change in internal resistance associated with change over time and change of temperature.
As a technique for efficiently generating a large current in a large-sized lithium ion secondary battery, PTL 1 proposes to form a current collector portion by sandwiching a tap portion (end portion) of a metal material (core member) constituting an electrode by a conductive member and welding the end portion to the conductive member.
On the other hand, PTL 2 proposes a battery in which an end portion of an electrode core member is made to protrude from an electrode group and the protruding portion is connected to a current collector plate. The current collector plate has a cutaway groove portion, and the current collector plate and a tip of the protruding portion are connected to each other on the periphery of the groove portion. According to this proposition, it seems that the connection area of the current collector plate with the protruding portion can be set smaller and the strength of the connection portion can be increased.
[Citation List]
[Patent Literature]
    [PTL 1] Japanese Laid-Open Patent Publication No. 7-263029    [PTL 2] Japanese Laid-Open Patent Publication No. 2003-36834